Spectrometers are often used to remotely determine the composition of or the physical properties of an object. A spectrometer collects reflected light or electromagnetic radiation from an object and separates the collected light or electromagnetic radiation into spectral components or separate wavelengths. The separate wavelengths are detected and are generally unique for a material or element. By analyzing the resultant spectrum, the properties of the object may be determined and the object may be identified. There is an increasing need to remotely identify objects, especially for the purpose of security so as to detect potentially dangerous objects, such as explosives or toxins. Accordingly, there has been much development in this field.
A spectrometer is disclosed in U.S. Pat. No. 6,977,727 issuing to Lerner on Dec. 20, 2005 and entitled Compact Imaging Spectrometer Utilizing Immersed Gratings. Therein disclosed is an imaging spectrometer having an entrance slit and a lens for refracting the light and delivering the light to an immersion diffraction grating. The diffracted light is again refracted and focused by the lens on the detector.
Another spectrometer is disclosed in U.S. Pat. No. 6,980,295 issuing to Lerner on Dec. 27, 2005 and entitled Compact Catadioptric Imaging Spectrometer Utilizing Reflective Grating. Therein disclosed is an imaging spectrometer having an entrance slit, an aspheric lens, grating, and detector.
Another spectrometer is disclosed in U.S. Pat. No. 6,985,226 issuing to Lerner on Jan. 10, 2006, and entitled Compact Imaging Spectrometer Utilizing an Immersed Grating and Anamorphic Mirror. Therein disclosed is an imaging spectrometer having an entrance slit, an anamorphic mirror, a grating, and a detector array.
Yet another spectrometer is disclosed in U.S. Pat. No. 7,006,217 issuing to Lerner on Feb. 28, 2006 and entitled Compact Catadioptric Imaging Spectrometer Utilizing Immersed Gratings. Therein disclosed is a spectrometer having an entrance slit, a catadioptric lens, a grating that diffracts the light back to the catadioptric lens and a detector.
Another spectrometer is disclosed in U.S. Pat. No. 7,016,037 issuing to Chrisp et al on Mar. 21, 2006 and entitled Imaging Spectrometer Utilizing Immersed Gratings With Accessible Entrance Slit, which is herein incorporated by reference. Therein disclosed is an imaging spectrometer, an entrance slit, a catadioptric lens with a mirrored surface, a grating, and a detector array. In one embodiment, an additional lens of zinc selenide is placed between the catadioptric lens made of germanium and the detector.
Yet another spectrometer is disclosed in U.S. Pat. No. 7,016,038 issuing to Chrisp et al on Mar. 21, 2006 and entitled Compact Imaging Spectrometer Utilizing Immersed Gratings. Therein disclosed is an imaging spectrometer having a dioptric lens in combination with an immersion diffraction grating that compensates for optical distortions.
Yet another spectrometer is disclosed in U.S. Pat. No. 7,041,979 issuing to Chrisp on May 9, 2006 and entitled Compact Reflective Imaging Spectrometer Utilizing Immersed Gratings. Therein disclosed is an imaging spectrometer using at least two mirrors.
Even though there has been substantial development in the field of imaging spectrometers recently, there is a need to continuously improve performance. Specifically, there is a need to provide a compact and efficient imaging spectrometer that has a relatively large field of view and that has an enhanced F-number.